The decay penetrates the enamel (white) of the tooth and works it way towards the pulp or nerve of the tooth (pink).

A tooth ache is usually caused when the nerve of the tooth becomes "irritated" by some form of stimulus. Usually this stimulus is either in the form of decay that has invaded the nerve, or trauma caused to the tooth.

How does decay affect the tooth? The tooth is an actual living structure in your body. The nerve sits in the middle of the tooth in an area called the pulp. this contains the nerve and blood supply to the tooth. When you get a cavity, the bacteria that causes the cavity starts to slowly eat away at the tooth working its way to the center of the tooth and the nerve. Most of the time this process is painless and goes unnoticed by the patient (Figure1). Sometimes patients may feel sensitivity to cold foods and beverages as well as sweets such as chocolate and candy. At this stage the cavity can usually be filled with the appropriate filling material and the sensitivity goes away.

The decay has grown and is closer to the nerve. The patient may experience a toothache with a cavity this size.

If the cavity is left untreated, the cavity will continue to grow and work its way to the center of the tooth (Figure 2). During this time the patient may or may not feel any symptoms. When a cavity becomes this large, the tooth is ideally treated with a crown instead of a simple filling because of the extensive missing tooth structure.

The decay has invaded the pulp of the tooth and an abscess is beginning to form at the ends of the root. At this stage the tooth needs to be treated with a root canal.

If the decay reaches the center of the pulp, then the pulp becomes infected (Figure 3). As the infection grows, it puts pressure on the nerve of the tooth and this causes a tooth ache. If the cavity reaches this stage, then a simple filling will not work. the nerve of the tooth needs to be removed. this is called a root canal.

Other times a tooth ache may be caused not by the nerve of the tooth but because the gum tissue around the tooth becomes infected. This infection called pericornitis is a common reason that wisdom teeth are removed.

Visit your doctor to determine the source of the toothache and what the appropriate treatment would be.